Resistor Basics

Created at: 2025-01-15

Laws

• Ohm's law: R = V/I

In Series

R(series) = R1 + R2

In Parallel

R(parallel) = (R1*R2) / (R1+R2)

Tip: By parallelising resistors you always get a smaller resistance.

Power (dissipated)

P = IV
P = I²R
P = V²/R

Intuition

• A large resistor in series with a small resistor has roughly the resistance of the larger one.
• Inversely, a large resistor in parallel with a small resistor has roughly the resistance of the smaller one.
• To reduce the resistance, connect a (much) larger resistor in parallel.
• Putting N resistors of value X in parallel is the same as having a resistor of value X/N

Trivia

• Usually made of some conducting stuff (carbon, thin metal, carbon film, wire of poor conductivity...) and characterised by its resistance.
• Most frequent resistors come in values from 1Ω to 10MΩ.
• Also characterised by how much power they can safely dissipate. Usually around 1/4W or 1/8W